Method and apparatus for training a learning machine

ABSTRACT

The disclosure relates to a method and apparatus for training a learning machine, wherein the apparatus includes: a broadcasting module for broadcasting an initial global model for a training cycle to a plurality of worker nodes; a receiving module for receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle; an aggregating module for aggregating the plurality of updated local models to obtain an aggregated model; and a generating module for generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.

TECHNICAL FIELD

The present disclosure relates generally to learning machine techniques and, more specifically, to a method and apparatus for training a learning machine.

BACKGROUND

Deep learning machines, including a deep neural network (DNN), a convolutional neural network (CNN), a recurrent neural network (RNN) and their variants, have become new state-of-the-art solutions for performing tasks such as speech recognition, image recognition, handwriting analysis and object classification.

A deep learning machine may be trained to perform a particular task using techniques such as mini-batch based stochastic gradient descent (SGD), asynchronous SGD, model averaging, a combination of asynchronous SGD and model averaging, etc. However, each of these techniques has drawbacks. For example, mini-batch based SGD is a sequential training procedure. Accordingly, training of deep learning machines using mini-batch based SGD is difficult to parallelize across multiple computing devices. Further, although techniques such as asynchronous SGD and model averaging may enable the parallelization of training across multiple computing nodes, the deep learning machines that are trained using such techniques generally produce results that are inferior to those produced using mini-batch based SGD.

SUMMARY

Embodiments of the disclosure provide a method and apparatus for training a learning machine, which may speed up training of the learning machine and improve accuracy of the learning machine.

According to an embodiment of the disclosure, a method for training a learning machine may include broadcasting an initial global model for a training cycle to a plurality of worker nodes. The method may also include receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle. The method may also include aggregating the plurality of updated local models to obtain an aggregated model. The method may also include generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.

According to an embodiment of the disclosure, an apparatus for training a learning machine may include a broadcasting module for broadcasting an initial global model for a training cycle to a plurality of worker nodes. The apparatus may also include a receiving module for receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle. The apparatus may also include an aggregating module for aggregating the plurality of updated local models to obtain an aggregated model. The apparatus may also include a generating module for generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature and advantages of the present disclosure will be more apparent from the detailed description set forth below when taken in conjunction with the drawings in which use of the same reference number in different figures indicates similar or identical items.

FIG. 1 illustrates an example system for training a learning machine according to an embodiment of the disclosure.

FIG. 2 illustrates an example method for training a learning machine according to an embodiment of the disclosure.

FIG. 3 illustrates a method for training a learning machine according to an embodiment of the disclosure.

FIG. 4 illustrates an apparatus for training a learning machine according to an embodiment of the disclosure.

FIG. 5 illustrates a device for training a learning machine according to an embodiment of the disclosure.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been illustrated or described in detail so as not to obscure the particular embodiments.

Various embodiments of the disclosure may provide techniques for training a learning machine, which may speed up training of the learning machine and improve accuracy (e.g., recognition accuracy of a classifier, regression accuracy of a regression machine, similarity score of a comparator, etc) of the learning machine. The learning machine may be any type of learning machines, including a deep learning machine (e.g., DNN, CNN, RNN or the like), a shallow learning machine (e.g., a support vector machine (SVM), a boosting machine, a logistic regression machine or the like), or the like.

FIG. 1 illustrates an example system for training a learning machine according to an embodiment of the disclosure. The example system 10 may include multiple computing devices 20 and one or more storage devices 30. The computing devices 20 may be coupled to the one or more storage devices 30. In an aspect, the computing devices 20 and storage devices 30 may be configured as a single computer system, or a computer cluster, or other architectures used in a cloud-computing infrastructure.

In an aspect, the computing devices 20 may include general purpose computers, such as desktop computers, tablet computers, laptop computers, servers, and so forth. In another aspect, the computing devices 20 may include smart phones, game consoles, or any other electronic devices. In still another aspect, the computing devices 20 may include various processors, such as central processor units (CPUs), graphics processor units (GPUs), other types of processors, or a combination of any of the above.

In an aspect, one of the computing devices 20 may act as a master node 21 while others of the computing devices 20 may act as worker nodes 22(1)-22(N), wherein N is a positive integer and represents the number of worker nodes. The master node 21 may control the worker nodes 22(1)-22(N) and the worker nodes 22(1)-22(N) may process data. In another aspect, the computing device that acts as the master node 21 may also act as one of the worker nodes. In an aspect, the master node 21 may communicate with the worker nodes 22(1)-22(N) via any wireless and/or wired communication technologies.

The one or more storage devices 30 may store training data 40. In an aspect, in the context of speech recognition, the training data 40 may be a speech corpus that includes a collection of speech samples from human speakers. For example, the speech corpus may include North American English speech samples collected from speakers of North American English in the United States and Canada, Chinese speech samples collected from speakers of Chinese in China, etc. In other aspects, the training data 40 may include images, handwriting samples, and/or other data.

FIG. 2 illustrates an example method for training a learning machine according to an embodiment of the disclosure. The example method shown in FIG. 2 will be described below in conjunction with the example system 10 shown in FIG. 1.

At block 202, the training data 40 stored in the one or more storage devices 30 may be partitioned, for example by the master node 21, into M data blocks. The M data blocks may each be further partitioned into N′ data splits each containing multiple mini-batches, wherein M and N′ are positive integers. In an aspect, the M data blocks do not overlap with each other, nor do N′ data splits of each data block. In this embodiment, N′ is equal to N, which is the number of the worker nodes as described above. Depending on the nature of training strategies of the learning machine being used, partitioning of the training data 40 may be done at frame, chunk or sequence level as appropriate for a given system.

At block 204, the master node 21 may provide, for example prior to a training iteration comprising M′ training cycles each using one of the M data blocks to train the learning machine, to each of the worker nodes 22(1)-22(N) M′ data splits of the training data 40 assigned to the worker node for the training iteration, wherein M′ is an integer larger than 1. In this embodiment, M′ is equal to M.

For example, if a data split P₁ included in the first data block of the training data 40 is assigned to a particular worker node 22(i) for the first training cycle of the training iteration, a data split P₂ included in the second data block of the training data 40 is assigned to the particular worker node 22(i) for the second training cycle of the training iteration, . . . , a data split P_(M′-1) included in the (M′−1)-th data block of the training data 40 is assigned to the particular worker node 22(i) for the (M′−1)-th training cycle of the training iteration, and a data split P_(M′) included in the M′-th data block of the training data 40 is assigned to the particular worker node 22(i) for the M′-th training cycle of the training iteration, the master node 21 may provide the data splits P₁, P₂, . . . , P_(M′-1) and P_(M′) to the particular worker node 22(i) prior to the training iteration.

In an aspect, providing the data splits to the worker nodes 22(1)-22(N) may be implemented in such a manner that the master node 21 may obtain, from the one or more storage devices 30, the M′ data splits assigned to each of the worker nodes 22(1)-22(N) and transmit the obtained M′ data splits to the corresponding worker node. In another aspect, providing the data splits to the worker nodes 22(1)-22(N) may implemented in such a manner that the master node 21 may obtain information on the M′ data splits assigned to each of the worker nodes 22(1)-22(N) and transmit the obtained information to the corresponding worker node, such that each of the worker nodes 22(1)-22(N) may obtain, from the one or more storage devices 30, the M′ data splits assigned to the worker node based on the information received from the master node 21.

At block 206, the master node 21 may broadcast, in a training cycle t of the training iteration (hereafter, the training cycle t may also be denoted as training cycle TC), an initial global model W_(g)(t−1) for the training cycle TC to the worker nodes 22(1)-22(N).

At block 208, each of the worker nodes 22(1)-22(N) may generate an updated local model independently based on the initial global model W_(g)(t−1) received from the master node 21 and the data split assigned to the worker node for the training cycle TC. Here, the data splits assigned to the worker nodes 22(1)-22(N) for the training cycle TC are from a data block of the training data 40 for the training cycle TC. In an aspect, the initial global model received from the master node 21 by each of the worker nodes 22(1)-22(N) may be used as an initial local model which is to be updated on that worker node.

In an aspect, each of the worker nodes 22(1)-22(N) may generate an updated local model independently by using one-sweep mini-batch based SGD with momentum trick. For example, assuming that the data split D_(tk) assigned to a worker node 22(k) of the worker nodes 22(1)-22(N) for the training cycle TC may contain τ mini-batches, wherein r is a positive integer, and w_(k)(t,ρ) may represent the fine-tuned local model after ρ mini-batches of the data split D_(tk) have been processed on the worker node 22(k), wherein ρ is a positive integer not larger than τ, w_(k)(t,ρ) may be calculated by the following equations (2):

w _(k)(t,0)=W _(g)(t−1)

v _(k)(t,0)=0

v _(k)(t,ρ)=ε·v _(k)(t,ρ=1)−(1−e)·γ·g(k,t,ρ)

w _(k)(t,ρ)=w _(k)(t,ρ−1)+v _(k)(t,ρ),  (2)

wherein ϵ, γ may represent a momentum and a learning rate, respectively; g(k, t, ρ) may represent a gradient of the ρ-th mini-batch of the data split D_(tk); and v_(k)(t,ρ) may represent a local model update on the worker node 22(k) after the ρ-th mini-batch of the data split D_(tk) is processed. The fine-tuned local model w_(k)(t,τ) after all τ mini-batches of the data split D_(tk) have been processed on the worker node 22(k) is the updated local model generated by the worker node 22(k).

In other aspects, each of the worker nodes 22(1)-22(N) may generate the updated local model independently based on the initial global model W_(g)(t−1) for the training cycle TC and the data split assigned to the worker node for the training cycle TC by other algorithms such as natural gradient SGD, asynchronous SGD, and so forth.

At block 210, each of the worker nodes 22(1)-22(N) may transmit the updated local model it has generated to the master node 21.

At block 212, the master node 21 may receive N updated local models from the worker nodes 22(1)-22(N).

At block 214, the master node 21 may aggregate the N updated local models to obtain an aggregated model denoted as W(t).

In an aspect, the aggregating of the N updated local models may comprise averaging the N updated local models by using the following equation (3) to obtain the aggregated model W(t).

$\begin{matrix} {{\overset{\_}{W}(t)} = {\frac{1}{N}{\sum\limits_{k = 1}^{N}\; {w_{k}\left( {t,\tau} \right)}}}} & (3) \end{matrix}$

In other aspects, aggregating the N updated local models may be implemented by any other suitable algorithms.

At block 216, the master node 21 may determine a first global model update G(t) by using the aggregated model W(t) and the initial global model W_(g)(t−1) for the training cycle TC. The first global model update G(t) may be calculated based on the following equation (4).

G(t)= W (t)−W _(g)(t−1)  (4)

The first global model update G(t) is a model update resulting from one data block for the training cycle TC, which includes N′ data splits, each being processed on a worker node.

At block 218, the master node 21 may determine a second global model update for the training cycle TC by using the first global model update G(t) and historical information obtained from a training cycle t−1 that precedes the training cycle TC. Hereafter, the training cycle t−1 may also be denoted as the preceding training cycle PC.

In an aspect, the second global model update, denoted as Δ(t), for the training cycle TC may be generated by the following equation (5):

Δ(t)=η_(t)·Δ(t−1)+ζ_(t) ·G(t),0<η_(t)<1,ζ_(t)>0  (5)

where Δ(t−1) is a second global model update for the preceding training cycle PC which, in an aspect of the disclosure, may represent the historical information obtained from the preceding training cycle PC; η_(t) is a block momentum for the training cycle TC; and ζ_(t) is a block learning rate for the training cycle TC. It may be appreciated that, in this aspect, the second global model update Δ(t) for the training cycle TC may represent the historical information obtained from the training cycle TC, which may be used in training cycle(s) following the training cycle TC.

In an aspect, ζ_(t) may be equal approximately to 1, and/or η_(t) may be set relatively small if the number of the training cycles in the training iteration is small. For example, η_(t) may be equal approximately to

$1 - \frac{1}{N}$

if the number of the training cycles in the training iteration is larger than a predefined threshold, and η_(t) may be equal to a value less than

$1 - \frac{1}{N}$

if the number of the training cycles in the training iteration is not larger than the predefined threshold. In an aspect, the predefined threshold may be set empirically.

In an aspect, ζ_(t) may have the same value for different training cycles, and/or η_(t) may have the same value for different training cycles. In another aspect, ζ_(t) may have different values for different training cycles, and/or η_(t) may have different values for different training cycles.

At block 220, the master node 21 may generate an updated global model for the training cycle TC by using an updated global model for the preceding training cycle PC and the second global model update for the training cycle TC. In an aspect, the updated global model W(t) for the training cycle TC may be generated by the following equation (6):

W(t)=W(t−1)+Δ(t)  (6)

where W(t−1) represents the updated global model for the preceding training cycle PC.

At block 222, the master node 21 may generate an initial global model W_(g)(t) for a training cycle t+1 that follows the training cycle TC. Hereafter, the training cycle t+1 may also be denoted as the following training cycle FC. The initial global model W_(g)(t) for the following training cycle FC will be broadcasted to the worker nodes 22(1)-22(N) by the master node 21 in the following training cycle FC.

In an aspect, the initial global model W_(g)(t) for the following training cycle FC may be generated based on the updated global model for the training cycle TC. For example, the initial global model W_(g)(t) for the following training cycle FC may be the updated global model for the training cycle TC. That is, the initial global model W_(g)(t) for the following training cycle FC may be calculated by the following equation (7).

W _(g)(t)=W(t)  (7)

In another aspect, the initial global model W_(g)(t) for the following training cycle FC may be generated based on the updated global model for the training cycle TC and the historical information obtained from the training cycle TC. For example, the initial global model W_(g)(t) for the following training cycle FC may be generated based on the updated global model for the training cycle TC and the second global model update for the training cycle TC by the following equation (8):

W _(g)(t)=W(t)+η_(t+1)·Δ(t)  (8)

where η_(t+1) is the block momentum for the following training cycle FC.

It can be appreciated from the above that the initial global model W_(g)(t−1) for the training cycle TC may be generated based on the updated global model for the preceding training cycle PC, or, may be generated based on the updated global model for the preceding training cycle PC and the historical information obtained from the preceding training cycle PC. For example, It can be appreciated from the equations (7) and (8) that the initial global model W_(g)(t−1) for the training cycle TC may be the updated global model for the preceding training cycle PC, or, may be generated based on the updated global model for the preceding training cycle PC and the second global model update for the preceding training cycle PC.

In an aspect, blocks 206 to 222 are repeated until the M′ training cycles of the training iteration are finished. After the M′ training cycles of the training iteration are finished, the master node 21 may determine whether a stopping criterion is satisfied. If it is determined that the stopping criterion is satisfied, the updated global model for the last training cycle of the training iteration may be used as the final global model W(T) for the learning machine. If it is determined that the stopping criterion is not satisfied, another training iteration including M′ training cycles is started to continue to train the learning machine.

Combination of the blocks 206-214 may achieve intra-block parallel optimization that utilizes multiple worker nodes 22(1)-22(N) to process data in parallel, thereby speeding up training of the learning machine. The equation (5) may be considered as doing a blockwise model update filtering (BMUF), in light of that it generates the second global model update for the training cycle TC by filtering the first global model update with the historical information from the preceding training cycle PC. The first global model update is the model update resulting from a single data block and is typically noisy. Filtering out of the noisy component of the first global model update with the historical information from the preceding training cycle PC serves to help stabilize learning process. As a result, accuracy of the learning machine trained based on the disclosure suffers from little degradation, compared to the learning machines trained by mini-batch based SGD. On the other hand, accuracy of the learning machine trained based on simple model averaging, which does not use historical information, suffers from significant degradation especially with more parallel worker nodes, compared to the learning machines trained based on the disclosure.

Those skilled in the art will appreciate that although partitioning of the training data 40 is performed by the master node 21 in the above embodiment, the disclosure is not so limited. In other embodiments of the disclosure, partitioning of the training data 40 may also be performed by other suitable devices prior to training of the learning machine.

Those skilled in the art will appreciate that although the historical information generated from the training cycle TC is the second global model update for the training cycle TC in the above embodiment, the disclosure is not so limited. For example, in an embodiment of the disclosure, the historical information from the training cycle TC may be generated based on information including but not limited to the second global model update for the training cycle TC. For example, the historical information from the training cycle TC may be generated based on the second global model update for the training cycle TC and second global model update(s) for training cycle(s) preceding the training cycle TC.

Those skilled in the art will appreciate that although the data splits of the training data 40 assigned to each of the worker nodes 22(1)-22(N) for the training iteration is provided to the worker node prior to the training iteration in the above embodiment, the disclosure is not so limited. In other embodiments of the disclosure, a data split of the training data 40 assigned to each of the worker nodes 22(1)-22(N) for any particular training cycle of the training iteration may be provided to the worker node by the master node 21 during the particular training cycle.

Those skilled in the art will also appreciate that although the initial global model for the following training cycle FC is generated in the training cycle TC in the above embodiment, the disclosure is not so limited. In other embodiments of the disclosure, for example, the initial global model for a training cycle may be generated at the beginning of the training cycle.

Those skilled in the art will also appreciate that although N′ is equal to N and M′ is equal to M in the above embodiment, the disclosure is not so limited. In other embodiments of the disclosure, N′ may be different from N and/or M′ may be different from M. For example, N′ is equal to 2N such that each worker node may process two data splits in a training cycle.

FIG. 3 illustrates a method for training a learning machine according to an embodiment of the disclosure. As an example, the method 300 shown in FIG. 3 may be implemented by the master node 21.

The method 300 may include, at block 302, broadcasting an initial global model for a training cycle to a plurality of worker nodes. The method 300 may also include, at block 304, receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle. The method 300 may also include, at block 306, aggregating the plurality of updated local models to obtain an aggregated model. The method 300 may also include, at block 308, generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.

In a first aspect, block 308 may include block 310, where a first global model update is determined based on the aggregated model and the initial global model for the training cycle. Block 308 may also include block 312, where a second global model update is determined based on the historical information from the preceding training cycle and the first global model update. Block 308 may also include block 314, where the updated global model for the training cycle is generated based on an updated global model for the preceding training cycle and the second global model update.

In a second aspect, the initial global model for the training cycle may be an updated global model for the preceding training cycle.

In a third aspect, the initial global model for the training cycle may be determined based on an updated global model for the preceding training cycle and the historical information from the preceding training cycle.

In a fourth aspect, each updated local model may be generated by one of the following algorithms: a one-sweep mini-batch stochastic gradient descent (SGD) with momentum trick, a natural gradient SGD, and an asynchronous SGD (ASGD).

In a fifth aspect, the method 300 may further include, at block 316, generating historical information from the training cycle based on the second global model update.

In a sixth aspect, the historical information from the training cycle Δ(t) may be generated by the following equation:

Δ(t)=η_(t)·Δ(t−1)+ζ_(t) ·G(t),0<η_(t)<1,ζ_(t)>0,

wherein Δ(t−1) represents the historical information from the preceding training cycle; G(t)=W(t)−W_(g)(t−1), wherein W(t) represents the aggregated model, and W_(g)(t−1) represents the initial global model for the training cycle; η_(t) is a block momentum for the training cycle; and ζ_(t) is a block learning rate for the training cycle.

In a seventh aspect, ζ_(t) may be equal approximately to 1.

In an eighth aspect, η_(t) may be set relatively small if the number of the training cycles in a training iteration is small.

In a ninth aspect, block 306 may further include averaging the plurality of updated local models to obtain the aggregated model.

In a tenth aspect, the method 300 may further include, at block 318, providing, prior to a training iteration comprising M′ training cycles, to each worker node M′ data splits that are assigned to the worker node for the training iteration, wherein M′ is an integer larger than 1.

FIG. 4 illustrates an apparatus for training a learning machine according to an embodiment of the disclosure.

The apparatus 400 may include a broadcasting module 402, a receiving module 404, an aggregating module 406 and a generating module 408. The broadcasting module 402 may be configured for broadcasting an initial global model for a training cycle to a plurality of worker nodes. The receiving module 404 may be configured for receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle. The aggregating module 406 may be configured for aggregating the plurality of updated local models to obtain an aggregated model. The generating module 408 may be configured for generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.

In a first aspect, the generating module 408 may include a first determining module 410, a second determining module 412 and an obtaining module 414. The first determining module 410 may be configured for determining a first global model update based on the aggregated model and the initial global model for the training cycle. The second determining module 412 may be configured for determining a second global model update based on the historical information from the preceding training cycle and the first global model update. The obtaining module 414 may be configured for generating the updated global model for the training cycle based on an updated global model for the preceding training cycle and the second global model update.

In a second aspect, the initial global model for the training cycle may be an updated global model for the preceding training cycle.

In a third aspect, the initial global model for the training cycle may be determined based on an updated global model for the preceding training cycle and the historical information from the preceding training cycle.

In a fourth aspect, each updated local model may be generated by one of the following algorithms: a one-sweep mini-batch stochastic gradient descent (SGD) with momentum trick, a natural gradient SGD, and an asynchronous SGD (ASGD).

In a fifth aspect, the apparatus 400 may further include: a second generating module 416 for generating historical information from the training cycle based on the second global model update.

In a sixth aspect, the historical information from the training cycle Δ(t) may be generated by the following equation:

Δ(t)=η_(t)·Δ(t−1)+ζ_(t) ·G(t),0<η_(t)<1,ζ_(t)>0,

wherein Δ(t−1) represents the historical information from the preceding training cycle; G(t)=W(t)−W_(g)(t−1), wherein W(t) represents the aggregated model, and W_(g)(t−1) represents the initial global model for the training cycle; η_(t) is a block momentum for the training cycle; and ζ_(t) is a block learning rate for the training cycle.

In a seventh aspect, ζ_(t) may be equal approximately to 1.

In an eighth aspect, η_(t) may be set relatively small if the number of the training cycles in a training iteration is small.

In a ninth aspect, the aggregating module 406 may be further configured for: averaging the plurality of updated local models to obtain the aggregated model.

In a tenth aspect, the apparatus 400 may further include a providing module 418 for providing, prior to a training iteration comprising M′ training cycles, to each worker node M′ data splits that are assigned to the worker node for the training iteration, wherein M′ is an integer larger than 1.

The various modules in FIG. 4 may be implemented as electronic hardware, computer software, or combination of both. To clearly illustrate this interchangeability of hardware and software, the modules have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constrains imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure.

The various modules in FIG. 4 may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessor in conjunction with a DSP core, or any other such configuration.

FIG. 5 illustrates a device for training a learning machine according to an embodiment of the disclosure. The device 500 shown in FIG. 5 may implement the master node 21, for example.

The device 500 may comprise one or more processors 510 and a memory 520 for storing computer-executable instructions that, when executed, cause the one or more processors 510 to perform acts included in the method 300. In an aspect, the modules included in the apparatus 400 may be embodied as the computer-executable instructions stored in the memory 520.

Embodiments of the disclosure may also provide a computer-readable medium having thereon computer-executable instructions that are executable to cause one or more processors to perform acts included in the method 300. In an aspect, the modules included in the apparatus 400 may be embodied as the computer-executable instructions on the computer-readable medium.

Embodiments of the disclosure may provide a method for training a learning machine. The method may comprise: broadcasting an initial global model for a training cycle to a plurality of worker nodes; receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle; aggregating the plurality of updated local models to obtain an aggregated model; and generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.

In an aspect, generating an updated global model for the training cycle may further comprise: determining a first global model update based on the aggregated model and the initial global model for the training cycle; determining a second global model update based on the historical information from the preceding training cycle and the first global model update; and generating the updated global model for the training cycle based on an updated global model for the preceding training cycle and the second global model update.

In an aspect, the initial global model for the training cycle is an updated global model for the preceding training cycle; or the initial global model for the training cycle is determined based on an updated global model for the preceding training cycle and the historical information from the preceding training cycle.

In an aspect, each updated local model is generated by one of the following algorithms: a one-sweep mini-batch stochastic gradient descent (SGD) with momentum trick, a natural gradient SGD, and an asynchronous SGD (ASGD).

In an aspect, the method may further comprise: generating historical information from the training cycle based on the second global model update.

In an aspect, the historical information from the training cycle Δ(t) is generated by the following equation:

Δ(t)=η_(t)·Δ(t−1)+ζ_(t) ·G(t),0<η_(t)<1,ζ_(t)>0,

wherein Δ(t−1) represents the historical information from the preceding training cycle; G(t)=W(t)−W_(g)(t−1), wherein W(t) represents the aggregated model, and W_(g)(t−1) represents the initial global model for the training cycle; η_(t) is a block momentum for the training cycle; and ζ_(t) is a block learning rate for the training cycle.

In an aspect, ζ_(t) is equal approximately to 1.

In an aspect, η_(t) is set relatively small if the number of the training cycles in a training iteration is small.

In an aspect, aggregating the plurality of updated local models may further comprise: averaging the plurality of updated local models to obtain the aggregated model.

In an aspect, the method may further comprise: providing, prior to a training iteration comprising M′ training cycles, to each worker node M′ data splits that are assigned to the worker node for the training iteration, wherein M′ is an integer larger than 1.

Embodiments of the disclosure may provide an apparatus for training a learning machine. The apparatus may comprise: a broadcasting module for broadcasting an initial global model for a training cycle to a plurality of worker nodes; a receiving module for receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle; an aggregating module for aggregating the plurality of updated local models to obtain an aggregated model; and a generating module for generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.

In an aspect, the generating module may be further configured for: determining a first global model update based on the aggregated model and the initial global model for the training cycle; determining a second global model update based on the historical information from the preceding training cycle and the first global model update; and generating the updated global mode for the training cycle based on an updated global model for the preceding training cycle and the second global model update.

In an aspect, the initial global model for the training cycle is an updated global model for the preceding training cycle; or the initial global model for the training cycle is determined based on the updated global model for the preceding training cycle and the historical information from the preceding training cycle.

In an aspect, the apparatus may further comprise: a module for generating historical information from the training cycle based on the second global model update.

In an aspect, the historical information from the training cycle Δ(t) is generated by the following equation:

Δ(t)=η_(t)·Δ(t−1)+ζ_(t) ·G(t),0<η_(t)<1,ζ_(t)>0,

wherein Δ(t−1) represents the historical information from the preceding training cycle; G(t)=W(t)−W_(g)(t−1), wherein W(t) represents the aggregated model, and W_(g)(t−1) represents the initial global model for the training cycle; η_(t) is a block momentum for the training cycle; and ζ_(t) is a block learning rate for the training cycle.

In an aspect, ζ₁ is equal approximately to 1.

In an aspect, η_(t) is set relatively small if the number of the training cycles in a training iteration is small.

In an aspect, the aggregating module is further configured for averaging the plurality of updated local models to obtain the aggregated model.

Embodiments of the disclosure may provide a device for training a learning machine. The device may comprise: one or more processors; and a memory storing computer-executable instructions that, when executed, cause the one or more processors to perform acts of the above method for training a learning machine.

Embodiments of the disclosure may provide a system. The system may comprise: one or more storage devices for storing training data for training a learning machine; a plurality of worker nodes; and a master node for performing acts of the above method for training a learning machine.

Although the various embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended representations is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed subject matter. 

1. A method for training a learning machine, comprising: broadcasting an initial global model for a training cycle to a plurality of worker nodes; receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle; aggregating the plurality of updated local models to obtain an aggregated model; and generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.
 2. The method of claim 1, wherein generating an updated global model for the training cycle further comprises: determining a first global model update based on the aggregated model and the initial global model for the training cycle; determining a second global model update based on the historical information from the preceding training cycle and the first global model update; generating the updated global model for the training cycle based on an updated global model for the preceding training cycle and the second global model update.
 3. The method of claim 1, wherein the initial global model for the training cycle is an updated global model for the preceding training cycle; or the initial global model for the training cycle is determined based on an updated global model for the preceding training cycle and the historical information from the preceding training cycle.
 4. The method of claim 1, wherein each updated local model is generated by one of the following algorithms: a one-sweep mini-batch stochastic gradient descent (SGD) with momentum trick, a natural gradient SGD, and an asynchronous SGD (ASGD).
 5. The method of claim 2, further comprising: generating historical information from the training cycle based on the second global model update.
 6. The method of claim 5, wherein the historical information from the training cycle Δ(t) is generated by the following equation: Δ(t)=η_(t)·Δ(t−1)+ζ_(t) ·G(t),0<η_(t)<1,ζ_(t)>0, wherein Δ(t−1) represents the historical information from the preceding training cycle, G(t)=W−W_(g)(t−1), wherein W(t) represents the aggregated model, and W_(g)(t−1) represents the initial global model for the training cycle, n_(t) is a block momentum for the training cycle, and ζ_(t) is a block learning rate for the training cycle.
 7. The method of claim 6, wherein ζ_(t) is equal approximately to
 1. 8. The method of claim 6, wherein n_(t) is set relatively small if the number of the training cycles in a training iteration is small.
 9. The method of claim 1, wherein aggregating the plurality of updated local models further comprises: averaging the plurality of updated local models to obtain the aggregated model.
 10. The method of claim 1, further comprising: providing, prior to a training iteration comprising M′ training cycles, to each worker node M′ data splits that are assigned to the worker node for the training iteration, wherein M′ is an integer larger than
 1. 11. An apparatus for training a learning machine, comprising: a broadcasting module for broadcasting an initial global model for a training cycle to a plurality of worker nodes; a receiving module for receiving a plurality of updated local models from the plurality of worker nodes, wherein each updated local model is generated by one of the plurality of worker nodes independently based on a data split assigned to the worker node and the initial global model for the training cycle; an aggregating module for aggregating the plurality of updated local models to obtain an aggregated model; and a generating module for generating an updated global model for the training cycle based at least on the aggregated model and historical information which is obtained from a preceding training cycle.
 12. The apparatus of claim 11, wherein the generating module is further configured for: determining a first global model update based on the aggregated model and the initial global model for the training cycle; determining a second global model update based on the historical information from the preceding training cycle and the first global model update; and generating the updated global mode for the training cycle based on an updated global model for the preceding training cycle and the second global model update.
 13. The apparatus of claim 11, wherein the initial global model for the training cycle is an updated global model for the preceding training cycle; or the initial global model for the training cycle is determined based on the updated global model for the preceding training cycle and the historical information from the preceding training cycle.
 14. The apparatus of claim 12, further comprising: a module for generating historical information from the training cycle based on the second global model update.
 15. The apparatus of claim 14, wherein the historical information from the training cycle Δ(t) is generated by the following equation: Δ(t)=η_(t)·Δ(t−1)+ζ_(t) ·G(t),0<η_(t)<1,ζ_(t)>0, wherein Δ(t−1) represents the historical information from the preceding training cycle, G(t)=W(t)−W_(g)(t−1), wherein W(t) represents the aggregated model, and W_(g)(t−1) represents the initial global model for the training cycle, n_(t) is a block momentum for the training cycle, and ζ_(t) is a block learning rate for the training cycle.
 16. The apparatus of claim 15, wherein ζ_(t) is equal approximately to
 1. 17. The apparatus of claim 15, wherein η_(t) is set relatively small if the number of the training cycles in a training iteration is small.
 18. The apparatus of claim 11, wherein the aggregating module is further configured for averaging the plurality of updated local models to obtain the aggregated model.
 19. A device for training a learning machine, comprising: one or more processors; and a memory storing computer-executable instructions that, when executed, cause the one or more processors to perform acts of claim
 1. 20. A system, comprising: one or more storage devices for storing training data for training a learning machine; a plurality of worker nodes; and a master node for performing acts of claim
 1. 